The Python code you write gets transformed into a Python function. E.g.,
CREATE FUNCTION myfunc(text) RETURNS text AS 'return args[0]' LANGUAGE plpythonu;
gets transformed into
def __plpython_procedure_myfunc_23456(): return args[0]
assuming that 23456 is the OID of the function.
If you do not provide a return value, Python returns the default None. The language module translates Python's None into the SQL null value.
The PostgreSQL function parameters are available in the global args list. In the myfunc example, args[0] contains whatever was passed in as the text argument. For myfunc2(text, integer), args[0] would contain the text argument and args[1] the integer argument.
The global dictionary SD is available to store data between function calls. This variable is private static data. The global dictionary GD is public data, available to all Python functions within a session. Use with care.
Each function gets its own execution environment in the Python interpreter, so that global data and function arguments from myfunc are not available to myfunc2. The exception is the data in the GD dictionary, as mentioned above.
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